1. Field of the Invention
The present invention relates to styrene-based polymer moldings and a process for production thereof. More particularly, it is concerned with styrene-based polymer moldings obtained by irradiating with electron rays moldings of styrene-based polymers having mainly syndiotactic configuration, and a process for efficiently producing the styrene-based polymer moldings.
2. Description of the Related Arts
A variety of resins are used in the production of electric or electronic parts. For example, in the case of connectors, the resins are often soldered for connection to lead wires, etc. The resins for producing these electric or electronic parts, are required to have heat resistance to such an extent that they are capable of maintaining their molding shapes even at a soldering temperature (usually more than 260.degree. C.). The heat resistance to such an extent is hereinafter referred to as "soldering resistance".
As resins having such soldering resistance, polyimides, polyphenylene sulfides, etc. are known. These resins, however, have an economical disadvantage of being expensive. On the contrary, although polyethylene terephthalates (PET), etc. are relatively inexpensive, they are not durable with soldering because of their poor heat resistance.
Resins which have excellent soldering resistance and thus are suitable for producing electric or electronic parts, and further which are inexpensive, have not been obtained.
Plastic bottles which have recently been increasingly used as containers for soft drinks, are produced by injection blow molding of PET. These plastic bottles, however, are difficult to use at temperatures exceeding the glass transition temperature (Tg) of PET. Thus it has been strongly desired to develop resins which are excellent in heat resistance and are suitable for production of food containers such as heat resistant plastic bottles for drinks.
The present inventor's group has developed styrene-based polymers, the main chain of which is mainly in the syndiotactic configuration (Japanese Patent Application Laid-Open No. 104818/1987). Among these styrene-based polymers, a styrene homopolymer has Tg of 100.degree. C., a melting point (Tm) of 260.degree. to 270.degree. C. and further is relatively inexpensive. Thus it is expected to be used for producing moldings, such as electric or electronic parts and food containers, with the aforementioned performance.
Under such circumstances, the present inventors' group proposed moldings of crystalline material as obtained by molding the aforementioned styrene-based polymers followed by heat treatment (specification of Japanese Patent Application No. 3846/1988). Further investigations, however, have revealed that the moldings are not always satisfactory as electric or electronic parts with high heat resistance because they have insufficient soldering resistance, although they are much superior to conventional moldings. Moreover, it proposed moldings as obtained by injection blow molding the aftermentioned styrene-based polymers (specification of Japanese Patent Application No. 3847/1988). These moldings, however, if not subjected to heat treatment, are not durable to hot water and steam at about 100.degree. C. In any case, it is difficult to obtain moldings suitable for food containers, etc. from the styrene-based polymers.